One of the frequent comments I hear from informed folk who've gone to the trouble to look at what we know about past climate cycles on earth: the hot and then the ice age, they come and go. That's true. Here's what I replied to one such reasonable correspondent: "the fact that there are recurring natural climate cycles does not preclude the evidence that some of the current rapid warming is enhanced by man-made pollution put into the air...the fact that an occasional massive volcanic eruption can cause short-term global cooling does not mean that man-made global cooling could never be triggered by massive nuclear explosions...even if we humans are totally blameless in the current warming trend and even if it is only a natural cycle, it is likely to have effects for which we are not preparing, and we might be able to lessen the warming by taking action, and even if we converted to non-fossil fuel and the warming continued, we would have cut down on much air pollution that has bad effects far beyond climate change...we dealt with the causes of acid rain and the growing ozone hole but this one is too tough?" We could take a very libertarian approach, those foolhardy enough to live in Houston, London or the Maldives, can take their chances. They don't have to live there.